Refactor animate for web and Apple platform motion

[sreejithraman]

Summary

• keep the shared motion gate in the automatically discovered animate skill
• route web work to the preserved pattern library and shared implementation checks
• add deployment-aware SwiftUI and UIKit guidance, including live Reduce Motion handling
• record the new platform routing in SOURCES.md

Why

The skill advertised general interface motion while its implementation guidance was web-specific. Platform routing keeps the strong existing web behavior and makes the supported native scope accurate without loading irrelevant details.

Effect

Web, SwiftUI, and UIKit motion requests now receive platform-specific guidance. Haptics-only and Android work remain outside this skill.

Verification

• skill quick validator passed
• git diff --check passed
• all 39 web pattern files match the web index
• four independent native/Gemini review rounds completed; accepted findings were fixed

Stack

Standalone PR against main.